U.S. patent number 8,966,940 [Application Number 11/911,166] was granted by the patent office on 2015-03-03 for process for producing glass bar.
This patent grant is currently assigned to The Fukukawa Electric Co., Ltd.. The grantee listed for this patent is Tetsuya Kumada, Yasuhiro Naka, Toshihiro Nakamura, Toshiaki Tateishi. Invention is credited to Tetsuya Kumada, Yasuhiro Naka, Toshihiro Nakamura, Toshiaki Tateishi.
United States Patent |
8,966,940 |
Kumada , et al. |
March 3, 2015 |
Process for producing glass bar
Abstract
In a heating drawing, a base material glass plate is heated and
softened in a heating furnace, and drawn to a desired thickness to
form a glass strip. In the heating drawing, the base material glass
plate is heated so that the base material glass plate has a
U-shaped temperature distribution in a width direction. Such
process can be realized through heating by a heating element which
has a non-heating portion at a position opposite to a central
portion of the base material glass plate in the width direction and
a heating portion on both sides of the non-heating portion. Thus
provided is a method of manufacturing a glass strip, the method
includes heating and softening the base material glass plate, and
drawing the base material glass plate to a desirable thickness to
form a glass strip, and is capable of manufacturing a thin,
rod-like glass strip with an excellent flatness.
Inventors: |
Kumada; Tetsuya (Tokyo,
JP), Naka; Yasuhiro (Tokyo, JP), Nakamura;
Toshihiro (Tokyo, JP), Tateishi; Toshiaki (Tokyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kumada; Tetsuya
Naka; Yasuhiro
Nakamura; Toshihiro
Tateishi; Toshiaki |
Tokyo
Tokyo
Tokyo
Tokyo |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
The Fukukawa Electric Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
38005861 |
Appl.
No.: |
11/911,166 |
Filed: |
November 1, 2006 |
PCT
Filed: |
November 01, 2006 |
PCT No.: |
PCT/JP2006/321883 |
371(c)(1),(2),(4) Date: |
October 10, 2007 |
PCT
Pub. No.: |
WO2007/052708 |
PCT
Pub. Date: |
May 10, 2007 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080216515 A1 |
Sep 11, 2008 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 1, 2005 [JP] |
|
|
2005-318085 |
|
Current U.S.
Class: |
65/94; 65/92;
65/95; 65/93 |
Current CPC
Class: |
C03B
23/047 (20130101); C03B 23/037 (20130101); B65G
2201/0294 (20130101) |
Current International
Class: |
C03B
23/04 (20060101); C03B 37/05 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
05116974 |
|
Mar 1991 |
|
JP |
|
5 116974 |
|
May 1993 |
|
JP |
|
8 183627 |
|
Jul 1996 |
|
JP |
|
8 183628 |
|
Jul 1996 |
|
JP |
|
11 199255 |
|
Jul 1999 |
|
JP |
|
2005-505482 |
|
Feb 2005 |
|
JP |
|
2006-221166 |
|
Aug 2006 |
|
JP |
|
WO 03/029156 |
|
Apr 2003 |
|
WO |
|
Other References
"JP 05-116974" Machine translation as provided by AIPN Japan Patent
office at
http://dossier1.ipdl.inpit.go.jp/AIPN/odse.sub.--top.sub.--fwi.ipdl?N0-
000=7401 on Jan. 14, 2010. cited by examiner .
"JP 05-116974" provided by United States Patent and Trademark
Office, Translated by: Schreiber Translations, Inc. date provided:
Jan. 2010. cited by examiner .
JP05116974 translation, Tooru Michimata, Method and Apparatus for
Manufacturing Thin Glass Sheet. United States Patent and Trademark
Office Washington, D.C. January 2010, Translated by: Schreiber
Translations, Inc. cited by examiner .
U.S. Appl. No. 12/336,573, filed Dec. 17, 2008, Tateishi, et al.
cited by applicant .
U.S. Appl. No. 12/275,576, filed Nov. 21, 2008, Orita, et al. cited
by applicant .
U.S. Appl. No. 13/452,428, filed Apr. 20, 2012, Nakamura, et al.
cited by applicant .
Office Action issued Jun. 11, 2013 in Japanese Patent Application
No. 2011-1 98816 with English language translation. cited by
applicant.
|
Primary Examiner: Franklin; Jodi C
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A method of manufacturing a glass strip comprising: heating and
softening a base material glass plate in a heating furnace; and
drawing the base material glass plate to a desirable thickness to
form a glass strip, wherein the heating furnace includes a
rectangular core tube through which the base material glass plate
passes, the core tube having a plurality of side surfaces, wherein
at least one of the plurality of side surfaces of the core tube
includes a plurality of heaters positioned along the outside of the
side surface, the plurality of heaters being arranged along a width
direction of the base material glass plate, wherein the base
material glass plate is heated by adjusting temperatures of the
plurality of heaters so that the base material glass plate has a
U-shaped temperature distribution in a width direction in a
meniscus portion from a position where melting starts to a position
of the inflection point formed at the time of drawing on the
contour of the base material glass plate, wherein the base material
glass plate is heated so that a viscosity ratio of a central
portion to a side portion in a highest temperature portion of the
base material glass plate in the width direction is larger than one
and not larger than 20, wherein the base material glass plate is
drawn while an aspect ratio in cross section of the base material
glass plate is substantially maintained, and so that the glass
strip has a flatness of not more than 10 .mu.m against a width of
20 mm of the glass strip, wherein the glass strip has an aspect
ratio in cross section equal to or higher than 50, and wherein the
plurality of heaters are arranged in parallel with only a width
direction of the base material glass plate.
2. The method of manufacturing a glass strip according to claim 1,
wherein a viscosity ratio of the central portion to the side
portion of the base material glass plate in the width direction is
equal to or larger than 3.4.
Description
TECHNICAL FIELD
The present invention relates to a method of manufacturing a thin,
rod-like glass strip through heating drawing of a thick, plate-like
base material glass plate.
BACKGROUND ART
Conventionally, improvements in flatness and surface roughness are
very important for a glass plate employed for substrates of
semiconductor devices, spacers for field-effect flat panel
displays, or substrates of magnetic disks. However, a float process
or a casting process currently typically used as a method of
manufacturing a glass plate produces glass plates with low flatness
when used to manufacture thin glass plates. Therefore, the glass
plate has to be finished to an appropriate flatness for the above
use through grinding and polishing of a significant amount of a
surface thereof. As a result, the glass plate after the grinding
has an extremely unfavorable surface roughness.
To solve the problem as described above, the ground glass plate
typically is subjected to the polishing twice, so that the surface
roughness is 0.5 nm after the first polishing, and approximately
0.1 nm after the second polishing. It is expected that a third
polishing will be required in addition to the above, since there
will be a demand for a product with higher precision in the next
generation. Therefore, an endeavor to improve the flatness of the
glass plate only through the grinding and polishing will end up in
more time and work for grinding and polishing, which eventually
leads to a higher equipment cost.
In view of the above, a method is devised to manufacture a thin
glass plate of a desirable thickness using a base material glass
plate with a predetermined thickness and an improved surface
roughness and by heating the base material glass plate to soften
the same and drawing the softened glass plate (see patent Document
1).
Further, in connection with the above method of manufacturing a
glass plate, a technique for eliminating local unevenness of the
thickness of a glass plate is disclosed, according to which, plural
coolers are arranged along a width direction of the glass plate,
and power of a heater placed at a position corresponding to an
uneven portion is adjusted, or the glass plate is cooled partially
in the width direction (see Patent Document 2). Patent Document 1:
Japanese Patent Application Laid-Open No. H11-199255 Patent
Document 2: Japanese Patent Application Laid-Open No. H8-183627
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
However, when a thin glass strip of 0.7 mm or less in thickness is
to be formed through heating, softening, and drawing of the base
material glass plate, for example, it is difficult to make a glass
strip with an even thickness in width direction, and the
conventional glass strip after the heating drawing has an
unfavorable flatness.
In view of the above, an object of the present invention is to
provide a method of manufacturing a glass strip by heating and
softening a base material glass plate in a heating furnace and
drawing the softened base glass plate to a desirable thickness to
thereby form a glass strip, capable of manufacturing a thin,
rod-like glass strip with an excellent flatness.
Means for Solving Problem
To solve the problems as described above and to achieve an object,
a method of manufacturing a glass strip according to the present
invention includes heating drawing for heating and softening a base
material glass plate in a heating furnace, and drawing the base
material glass plate to a desirable thickness to form a glass
strip, wherein the base material glass plate is heated in the
heating drawing so that the base material glass plate has a
U-shaped temperature distribution in a width direction.
Further, in the method of manufacturing a glass strip according to
the present invention, the base material glass plate may be heated
in the heating drawing so that a viscosity ratio of a central
portion to a side portion of the base material glass plate in the
width direction is larger than one and not larger than 20.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing by a heating element which has
a non-heating portion at a position opposite to a central portion
of the base material glass plate in the width direction and a
heating portion on both sides of the non-heating portion.
Still further, a method of manufacturing a glass strip according to
the present invention includes heating drawing for heating and
softening a base material glass plate in a heating furnace, drawing
the base material glass plate to a desirable thickness to form a
glass strip, wherein the base material glass plate is heated in the
heating drawing so that a length of the base material glass plate
from a position where melting starts to a position of an inflection
point formed at a time of drawing on a contour of the base material
glass plate is equal to or longer than two-thirds a width of the
base material glass plate.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing so that the length of the base
material glass plate from the position where melting starts to the
position of the inflection point formed at the time of drawing on
the contour of the base material glass plate is equal to or shorter
than 1.5 times the width of the base material glass plate.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing so that the base material
glass plate has a U-shaped temperature distribution in the width
direction.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing so that a viscosity ratio of a
central portion to a side portion of the base material glass plate
in the width direction is larger than one and not larger than
20.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing by a heating element which has
a non-heating portion at a position opposite to a central portion
of the base material glass plate in the width direction and a
heating portion on both sides of the non-heating portion.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing so that at least a portion of
the base material glass plate from the position where melting
starts to the position of the inflection point formed at the time
of the drawing on the contour of the base material glass plate has
a U-shaped temperature distribution in the width direction.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be heated in the heating drawing so that at least a portion of
the base material glass plate from a position where melting starts
to a position of a distortion point temperature is placed in the
heating furnace.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may have a thermal expansion coefficient equal to or lower than
32.times.10.sup.-7(1/k).
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be made of borosilicate glass or quartz glass.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be drawn in the heating drawing so that the glass strip has a
aspect ratio in cross section equal to or higher than 50.
Still further, in the method of manufacturing a glass strip
according to the present invention, the base material glass plate
may be drawn in the heating drawing so that the glass strip has a
thickness equal to or lower than 0.7 mm.
Effect of the Invention
According to the present invention, difference in glass flow
generated in a central portion and a side portion of the base
material glass plate in a width direction at the time of heating
drawing is compensated by heating of the base material glass plate
in such a manner that the U-shaped temperature distribution is
generated in the width direction and generation of difference in
glass viscosity between the central portion and the side portion in
the width direction of the base material glass plate. Thus, the
speed of glass flow can be balanced, and the thickness of the glass
strip in the width direction can be made uniform, whereby the glass
strip with an excellent flatness can be manufactured.
Further, according to the present invention, the difference in the
speed of glass flow between the central portion and the side
portion of the base material glass plate is suppressed when the
heating is performed in the heating drawing so that the length from
a position where the melting of the base material glass plate
starts to a position of an inflection point formed at the time of
drawing on a contour of the base material glass plate is equal to
or longer than two-thirds the width of the base material glass
plate, whereby the thickness of the glass strip in the width
direction can be made uniform, and a glass strip with an excellent
flatness can be manufactured.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of a heating drawing apparatus
employed in a method of manufacturing a glass strip according to an
embodiment of the present invention.
FIG. 2 is a sectional view of a heating furnace shown in FIG.
1.
FIG. 3 is a plan view of the heating furnace shown in FIG. 1.
FIG. 4 is a graph of temperature distribution of a base material
glass plate in a width direction shown in association with
arrangement of heaters relative to the base material glass
plate.
FIG. 5 is a schematic diagram of heaters where a carbon block is
arranged in place of a heater in a central portion.
FIG. 6 is an explanatory diagram for explaining a method of
manufacturing a glass strip according to another embodiment of the
present invention.
FIG. 7 is a plan view of a heating furnace employed in a method of
manufacturing a glass strip according to still another embodiment
of the present invention.
FIG. 8 is a plan view of a heating furnace employed for a method of
manufacturing a glass strip according to still another embodiment
of the present invention.
FIG. 9 is a table of examples 1 to 5 and a comparative example
1.
FIG. 10 is a table of examples 6 to 8 and a comparative example
2.
FIG. 11 is a table of examples 9 to 11.
EXPLANATIONS OF LETTERS OR NUMERALS
1 Base material glass plate 5 Guide roll 7 Outer shape measuring
device 8 Protective-film coating device 9 Tension measuring device
10, 40, 60 Heating furnace 11 Glass strip 13, 14 Feedback path 15a
to 15f Heater 16 Furnace casing 17 Core tube 18 Carbon block 19
Structure 20 Base material transfer mechanism 21 Cutter 22 Meniscus
length 23 Width of base material glass plate 24 Heat zone length 25
Meniscus portion 30 Pulling-out mechanism 50 Heating drawing
apparatus
BEST MODE(S) FOR CARRYING OUT THE INVENTION
Exemplary embodiments of a method of manufacturing a glass strip
according to the present invention will be described in detail
below with reference to the accompanying drawings. The present
invention is not limited by the embodiments.
First Embodiment
FIG. 1 is a perspective view of a heating drawing apparatus
employed for a method of manufacturing a glass strip according to
an embodiment of the present invention. A heating drawing apparatus
50 includes a heating furnace 10 which is an electric resistance
furnace heating a base material glass plate 1, a base material
transfer mechanism 20 which transfers the base material glass plate
1 into the heating furnace 10, and a pulling-out mechanism 30 which
pulls out a glass strip 11 from the heating furnace 10. The heating
furnace 10 is provided with plural heaters not shown as heating
units that heat the base material glass plate 1. Further, at a
lower portion of the heating furnace 10, an outer shape measuring
device 7 that measures an outer shape of the glass strip 11, a
protective-film coating device 8 that applies a protective film on
a surface of the glass strip 11, a tension measuring device 9 that
measures tension of pulling of the glass strip 11, and a guide roll
5 that prevents twisting of the glass strip 11 are provided.
Further, at a lower portion of the pulling-out mechanism 30, a
cutter 21 is provided for carving a groove on a surface of the
glass strip and breaking the glass strip into a predetermined
length. Measurement values obtained by the outer shape measuring
device 7 are fed back to the base material transfer mechanism 20
through a feedback path 13. The base material transfer mechanism 20
controls a speed of base material transfer based on the feedback
value. Further, the measurement values are also fed back to the
pulling-out mechanism 30 through a feedback path 14. The
pulling-out mechanism 30 controls a pulling-out speed based on the
feedback value.
FIG. 2 is a sectional view of the heating furnace 10 shown in FIG.
1; and FIG. 3 is a plan view of the heating furnace 10 shown in
FIG. 1. The base material glass plate 1 is arranged inside a
rectangular core tube 17 in a furnace casing 16. Around the core
tube 17, plural heaters 15a, 15b, and 15c are arranged. For
example, a carbon resistance heating element is employed as the
heater. Further, a circumference of the heater is protected by an
inert gas to prevent the wasting of the heater.
The base material glass plate starts softening and melting when
subjected to heating at a temperature equal to or higher than a
softening point, and the width thereof contracts and the base
material glass plate is drawn. At the time of drawing, an
inflection point is formed on the contour of the base material
glass plate, and thereafter, the glass strip having a desirable
thickness and width is formed. A portion from a position where the
base material glass plate starts melting to a position of the
inflection point is called meniscus portion, and a length thereof
is called meniscus length. In the meniscus portion, glass flows
differently in a central portion and a side portion of the base
material glass plate in a width direction.
In the present invention, the base material glass plate is heated
in a heating drawing process in such a manner that the base
material glass plate has a U-shaped temperature distribution in the
width direction. Since the side portion of the base material glass
plate is higher in temperature than the central portion, the
viscosity of the glass becomes even lower and the speed of glass
flow increases. Thus, in the meniscus portion of the base material
glass plate, the difference in glass flow generated between the
central portion and the side portion in the width direction is
compensated by the difference in glass viscosity, and the speed of
the glass flow is balanced, whereby the thickness of the glass
strip in the width direction is made uniform and the glass strip
with an excellent flatness can be manufactured.
FIG. 4 is a graph of temperature distribution of the base material
glass plate in the width direction in the heating furnace shown in
FIG. 2 shown in association with arrangement of heaters relative to
the base material glass plate. An abscissa of the graph represents
temperature-measurement position of the base material glass plate,
whereas an ordinate represents relative temperature of the base
material glass plate at the measurement position. In a lower
portion of the graph, an arrangement of the heaters is shown
relative to the base material glass plate. When the heater 15b at a
position opposite to the central portion of the base material glass
plate is made lower in temperature than the heaters 15a and 15c to
the sides thereof, the base material glass plate can be heated so
as to have a U-shaped temperature distribution in the width
direction as shown in the graph.
As described above, the U-shaped temperature distribution in the
width direction of the base material glass plate can be achieved
through the heating when the power of the heater 15b at the central
portion shown in FIG. 2 is not turned on, or when a carbon block 18
is arranged in place of the heater 15b as shown in FIG. 5. Thus,
when the heating is performed with the use of a heating element
having a non-heating portion at a position opposite to the central
portion of the base material glass plate in the width direction,
and having heating portions at both sides of the non-heating
portion, the temperature difference between the central portion and
the side portion of the base material glass plate can be further
increased, so as to increase the difference in glass viscosity.
Further, the use of a heat-insulating material having higher heat
conductivity as a heat insulator arranged outside the core tube of
the furnace can also increase the temperature difference. For
example, a box configured with a carbon block filled with carbon
fibers can be used as the heat-insulating material. Such a
heat-insulating material may have heat conductivity of 0.4 to 4
W/mk or more.
Second Embodiment
Another embodiment of the present invention will be described. The
first embodiment described above realizes the manufacture of a
glass strip with an excellent flatness by defining the temperature
distribution of the base material glass plate in the width
direction. The another embodiment realizes the manufacture of a
glass strip with an excellent flatness by defining a relation
between temperature distribution in the heating furnace in a
drawing direction of the base material glass plate and the width of
the base material glass plate.
FIG. 6 is an explanatory diagram for explaining a method of
manufacturing a glass strip according to the another embodiment of
the present invention. According to the another embodiment, heating
is performed in a heating drawing process so that the length from a
position where the base material glass plate starts melting to a
position of an inflection point formed at the time of drawing on
the contour of the base material glass plate, in other words, a
meniscus length 22, is equal to or longer than two-thirds a width
23 of the base material glass plate. Then, the meniscus portion of
the base material glass plate is sufficiently long, and smaller
gradient is formed on the side portion when the width of the glass
plate contracts, whereby the difference in speed of glass flow
between the central portion and the side portion does not increase.
Therefore, the thickness of the glass strip in the width direction
can be made uniform, whereby the glass strip with an excellent
flatness can be manufactured.
The meniscus length 22 can be adjusted appropriately through the
adjustment of the heater length and the length of a heat zone in
the drawing direction of the base material glass plate in the
heating furnace; when the heat zone is made longer, the meniscus
length 22 can be made longer, accordingly. Further, the meniscus
length can be made longer when the pulling-out speed is increased.
Here, "heat zone" means a portion where the temperature in the
heating furnace is equal to or higher than a softening point of the
used glass as shown in FIG. 6, and "heat zone length" is a length
24 of the heat zone of the base material glass plate in the drawing
direction. The viscosity of the base material glass plate is
minimal in a portion where the temperature is highest, and the
inflection point is formed on the contour of this portion. A point
where the glass is of the highest temperature is determined by a
combination of the heat zone and the pulling-out speed.
Therefore, when the length and the arrangement of the heaters 15a,
15b, and 15c are appropriately adjusted, the length of a portion
extending from the upper end of the heat zone to a portion of the
highest temperature, and the heat zone length are adjusted, whereby
the heating can be performed so that a length from the point where
the base material glass plate starts melting to a position of the
inflection point, which is formed at a time of the drawing, on the
contour of the base material glass plate is equal to or longer than
two-thirds the width of the base material glass plate. Further, in
the second embodiment, the heaters 15a, 15b, and 15c may be set to
the same temperature, so that the base material glass plate is
heated so as to have an even temperature distribution in the width
direction. Alternatively, however, when the heater 15b is set to a
lower temperature than the temperature of the heaters 15a and 15c,
or when the heater 15bs is not powered, or when a carbon block is
installed instead of the heater 15b, so that the base material
glass plate is heated so as to have a U-shaped temperature
distribution in the width direction, the thickness of the glass
strip in the width direction can be made even more uniform, whereby
a glass strip with an even more excellent flatness can be
manufactured.
Third Embodiment
Still another embodiment of the present invention will be
described. The first embodiment described above achieves the
manufacture of a glass strip with an excellent flatness by defining
the temperature distribution of the base material glass plate in
the width direction. The second embodiment achieves the manufacture
of a glass strip with an excellent flatness by defining the
relation between the temperature distribution in the heating
furnace in the drawing direction of the base material glass plate
and the width of the base material glass plate. The third
embodiment achieves manufacture of a glass strip with an even more
excellent flatness with a high heating efficiency by combining the
above two and additionally defining a position where the
temperature distribution in the width direction is defined.
FIG. 7 is a plan view of a heating furnace employed in a method of
manufacturing a glass strip according to the still another
embodiment of the present invention. A heating furnace 40 having
heaters 15d, 15e, and 15f with relatively short heater length is
employed, and a base material glass plate is heated by the heaters
15d and 15f so that at least a portion extending from a position
where the base material glass plate starts melting to a position of
an inflection point formed at a time of the drawing on the contour
of the base material glass plate, in other words, a meniscus
portion 25, has a U-shaped temperature distribution in the width
direction of the base material glass plate. Further, with the
arrangement of the heater 15e with relatively short heater length
at a position lower than the portion 25, the base material glass
plate is heated so that the length from the position where the base
material glass plate starts melting to the position of the
inflection point formed at the time of the drawing on the contour
of the base material glass plate is equal to or longer than
two-thirds the width of the base material glass plate. Then, even
if the heater length of each heater is short, the thickness of the
glass strip in the width direction can be made even more uniform,
whereby a glass strip with an even more excellent flatness can be
manufactured.
The position of the inflection point of the contour of the base
material glass plate is a point where the viscosity of the glass is
minimum in the drawing direction, and the glass is cooled and
annealed in a portion below this point. Therefore, at a portion
below the inflection point, even if the length of the heaters on
two sides is made longer so as to form the U-shaped temperature
distribution in the width direction, there is relatively little
influence on the flatness of the resulting glass strip. In brief,
an important point is that the portion from the position where the
base material glass plate starts melting to the position of the
inflection point on the contour is heated so as to have the
U-shaped temperature distribution in the width direction, and the
heaters with necessary length for the purpose are used on two
sides. On the other hand, the central portion of the base material
glass plate, i.e., an upper portion of the heat zone can be heated
sufficiently by the heaters on two sides. Therefore, the heater at
the center does not need to be long enough to reach the upper
portion. As far as the heater is arranged at a lower position than
the heaters on two sides and at such a position that the highest
temperature portion of the heat zone can be formed at a lower
position, even if the heater length of the used heater is
relatively short, the heating can be performed so that the length
from the position where the base material glass plate starts
melting to the position of the inflection point formed at the time
of the drawing on the contour of the base material glass plate is
equal to or longer than two-thirds the width of the base material
glass plate.
Fourth Embodiment
Still another embodiment of the present invention will be
described. The first to the third embodiments described above
achieve the manufacture of a glass strip with an excellent flatness
by making the thickness of the glass strip uniform in the width
direction. The fourth embodiment can be combined with any of the
above embodiments, and relates to a method of manufacturing a glass
strip while preventing a distortion of the glass strip.
FIG. 8 is a plan view of a heating furnace used in the method of
manufacturing a glass strip according to the still another
embodiment of the present invention. A heating furnace 60 in which
an extended structure 19 surrounds a lower portion of the heating
furnace 10 is employed, so that a portion of the base material
glass plate extending from a position where melting starts to a
position of a distortion point temperature is placed in the heating
furnace during heating. With such an arrangement, the glass strip
is not cooled suddenly to a temperature equal to or lower than the
distortion point temperature at a time the glass strip is pulled
out from the heating furnace to an atmosphere, whereby the
distortion does not occur. In addition, it is possible to increase
the pulling-out speed of the glass strip. Preferably, a portion of
the base material glass plate extending from the position where the
melting starts to a position where the temperature is lower than
the distortion point temperature of the base material glass plate
by 50.degree. C. or, more preferably 100.degree. C., is placed in
the heating furnace during the heating, since such an arrangement
securely prevents the distortion.
Examples of the method of manufacturing a glass strip according to
the present invention will be described in detail below. The
present invention, however, is not limited by the examples.
Examples 1 to 5 & Comparative Example 1
As an example of the present invention, a base material glass plate
of 328 mm in width, 5 mm in thickness, and approximately 1.5 m in
length is prepared from borosilicate glass (TEMPAX Float.RTM.
manufactured by Schott AG) or quartz. The prepared base material
glass plate is subjected to heating drawing, and a glass strip is
manufactured. As a heating furnace, one with three heaters arranged
on two sides of the base material glass plate as shown in FIG. 2,
or one with an extended structure surrounding a lower portion of
the furnace as shown in FIG. 8 is employed. The employed heater is
620 mm in length and 256 mm in width. The heaters are arranged so
that the distance between center lines of the heaters is 277 mm.
Drawing conditions are: pulling-out speed is 4 m/min, width after
drawing is 25 mm, and thickness is 0.38 mm. Aspect ratio in cross
section is 66. Here, "aspect ratio in cross section" is a ratio of
width to thickness in a cross section of the glass plate. When the
aspect ratio in cross section of the glass strip is equal to or
more than 50, or when the thickness is equal to or lower than 0.7
mm, or both, an effect of the present invention, i.e., an
improvement of the flatness becomes even more prominent.
Examples 1 to 5 and a comparative example 1 shown in FIG. 9 will be
described below. In the example 1, the temperature of the central
heater is set to 900.degree. C. and the temperature of the side
heaters each is set to 1010.degree. C. in the heating furnace of
FIG. 2. The temperature of the base material glass plate is
915.degree. C. in the central portion and 945.degree. C. in two
side portions, thereby making a U-shaped temperature distribution
with temperature difference of 30.degree. C. Though a glass strip
manufactured under the above conditions has a concave-lens-like
section, the flatness is 5 .mu.m against plate width of 20 mm,
showing a favorable level. Here, "flatness" means a height
difference in a vertical direction between a highest point and a
lowest point at two points distanced from each other by an
arbitrary unit length on a substrate surface, when a glass strip is
cut off as a substrate having a necessary area and placed on a
horizontal plane. In the above, the unit length is the plate width,
i.e., 20 mm.
On the other hand, in the comparative example 1, the temperature of
the central heater and the side heaters are set equally to
1000.degree. C. in the heating furnace of FIG. 2. The temperature
of the base material glass plate is 985.degree. C. in the central
portion, and 980.degree. C. in the side portions, showing little
temperature difference. A glass strip manufactured under such
conditions shows a prominent concave-lens shape in cross section
and has a large value of flatness of 40 .mu.m against the plate
width of 20 mm.
In the example 2, in the heating furnace of FIG. 2, the central
heater is not powered, and a box configured with a carbon block
filled with carbon fibers is used outside the core tube as a heat
insulating member for the furnace. Heat conductivity of the heat
insulating member is 0.4 to 4 W/mk. Thus, the temperature
difference between the central portion and the side portion of the
base material glass plate in the width direction is set to
60.degree. which is higher than that in the example 1. Here,
viscosity ratio of the central portion to the side portion of the
base material glass plate in the width direction is 11.6. A glass
strip manufactured under such conditions has a favorable flatness
of 3 .mu.m against the plate width of 20 mm.
On the other hand, in the example 3, the central heater is not
powered, similarly to the example 2, and a member with heat
conductivity equal to or higher than 4 W/mk is employed as a heat
insulating member. The temperature difference between the central
portion and the side portion of the base material glass plate in
the width direction is set to 80.degree. C. which is higher than
that in the example 1 or 2. The viscosity ratio of the central
portion to the side portion of the base material glass plate in the
width direction is 26.3. A glass strip manufactured under such
conditions has a flatness of 10 .mu.m against the plate width of 20
mm, which is an improvement over the comparative example 1, though
the value is larger than that in the example 1 or 2. Further, the
sectional area of the glass strip is of an upward-convex shape.
When the temperature of the central portion of the base material
glass plate is lowered in excess, the viscosity shows an excessive
increase, whereby the flatness is deteriorated adversely. Based on
the results, it is found that the heating is preferably performed
so that the viscosity ratio of the central portion to the side
portion of the base material glass plate in the width direction is
larger than 1 and not larger than 20.
The example 4 employs a base material glass plate of quartz. In the
heating furnace of FIG. 2, the temperature of the central heater is
set to 1780.degree. C., and the temperature of the side heaters
each is set to 2020.degree. C. The temperature of the base material
glass plate is 1790.degree. C. in the central portion, and is
1950.degree. C. in the side portion, thereby showing a U-shaped
temperature distribution with the temperature difference of
160.degree. C. A glass strip manufactured under such conditions has
a favorable flatness of 2 .mu.m against the plate width of 20 mm.
As can be seen from the above, when the base material glass plate
is made of a material such as TEMPAX Float.RTM. or quartz having a
thermal expansion coefficient of 32.times.10.sup.-7 (1/k) or less,
even when the process is likely to cause temperature difference
between the front side and the back side of the glass plate as when
the rectangular furnace is employed, there is little difference in
stretch amount of the glass plate at the front side and the back
side, whereby the glass plate is less likely to be distorted due to
thermal expansion, and a more flat glass strip can be manufactured.
Further, since sudden heating or cooling does not cause cracking,
the glass strip can be pulled out at higher speed.
In the example 5, an extended structure surrounds the lower portion
of the furnace as shown in FIG. 8. The pulling-out speed is 7
m/min. The furnace is surrounded by the structure up to a portion
1.5 m below the lower end of the heater, and therefore, the drawn
glass strip can be gradually cooled before pulled out from the
heating furnace and cooled suddenly by the atmosphere. Thus, the
glass strip can be gradually cooled down to 510.degree. C. which is
a distortion point temperature of TEMPAX Float.RTM.. When the
structure made as an extension of the lower portion of the furnace
is employed, no distortion occurs in the glass strip even when the
pulling-out speed is increased. In addition, the glass strip has a
favorable flatness of 5 .mu.m against the plate width of 20 mm.
Examples 6 to 8 & Comparative Example 2
As an example of the present invention, a base material glass plate
of 328 mm in width, 5 mm in thickness, and approximately 1.5 m in
length is prepared from TEMPAX Float.RTM. whose softening point is
820.degree. C. The prepared base material glass plate is subjected
to heating drawing, and a glass strip is manufactured. As a heating
furnace, one with three heaters arranged on two sides of the base
material glass plate as shown in FIG. 2 is employed. The
temperature of each heater is set to 1000.degree. C. Here, the
temperature of the base material glass plate is 985.degree. C. in
the central portion, and 980.degree. in the side portions, with
little temperature difference. As a drawing condition, the
pulling-out speed is set to 7 m/min.
Examples 6 to 8 and a comparative example 2 shown in FIG. 10 will
be described. The example 6 adjusts the heat zone length by setting
an appropriate heater length, and heats the base material glass
plate so that the meniscus length is 1.2 times the width of the
base material glass plate (base material width). A glass strip
manufactured under such conditions shows a favorable flatness of 5
.mu.m against the plate width of 20 mm.
On the other hand, the comparative example 2 heats the base
material glass plate so that the meniscus length is 0.61 time the
base material width. A glass strip manufactured under such
conditions has a large value of flatness of 40 .mu.m against the
plate width of 20 mm.
The example 7 employs a wide base material glass plate and heats
the base material glass plate so that the meniscus length is 0.68
time the base material width. A glass strip manufactured under such
conditions shows a favorable flatness of 5 .mu.m against the plate
width of 60 mm. In other words, it is found that regardless of the
width of the base material glass plate, a glass strip with an
excellent flatness can be manufactured if the base material glass
plate is heated so that the length of the base material glass plate
from a position where melting starts to a position of an inflection
point formed at a time of the drawing on the contour of the base
material glass plate (i.e., meniscus length) is equal to or longer
than two-thirds the width of the base material glass plate.
The example 8 heats the base material glass plate so that the
meniscus length is 1.5 times the width of the base material glass
plate (base material width). A glass strip manufactured under such
conditions shows a favorable flatness of 5 .mu.m against the plate
width of 20 mm. In this case, however, it is found that the shape
of the glass strip responds to an adjustment of the manufacturing
conditions more slowly, and sometimes it is difficult to adjust
average values of the width or the thickness of the glass strips
through fine adjustment of the pulling-out speed. Based on the
results, it is found that when the heating is performed so that the
length of the base material glass plate from a position where the
melting starts to a position of the inflection point formed at a
time of the drawing on the contour of the base material glass plate
(i.e., meniscus length) is equal to or shorter than 1.5 times the
width of the base material glass plate, a glass strip whose width
and thickness are accurately controlled can be manufactured.
Examples 9 to 11
As an example of the present invention, a base material glass plate
of 328 mm in width, 5 mm in thickness, and approximately 1.5 m in
length is prepared from TEMPAX Float.RTM.. The prepared base
material glass plate is subjected to heating drawing, and a glass
strip is manufactured. As a heating furnace, one with three heaters
arranged on two sides of the base material glass plate as shown in
FIG. 2, or with heaters having a relatively short heater length as
shown in FIG. 7 is employed. Each heater is 256 mm in width. As
drawing conditions, the pulling-out speed is set to 7 m/min, the
width and thickness after the drawing is set to 25 mm and 0.38 mm.
The aspect ratio in cross section is 66.
Examples 9 to 11 shown in FIG. 11 will be described below. The
example 9 employing the heating furnace of FIG. 2 adjusts the heat
zone length by setting the temperature of the central heater to
875.degree. C., and the temperature of the side heaters to
1055.degree. C., and setting an appropriate heater length, and
heats the base material glass plate so that the meniscus length is
0.88 time the width of the base material glass plate (base material
width). The temperature of the base material glass plate is
920.degree. C. in the central portion, and 980.degree. C. in the
side portions, showing a U-shaped temperature distribution with the
temperature difference of 60.degree. C. A glass strip manufactured
under such conditions has a highly favorable flatness of 1 .mu.m
against the plate width of 20 mm.
The example 10, similarly to the example 9, sets the temperature of
the central heater to 875.degree. C. and the temperature of the
side heaters to 1055.degree. C. in the heating furnace of FIG. 2,
while setting the heater length slightly shorter, and the heating
is performed so that the meniscus length is 0.61 time the base
material width. A glass strip manufactured under such conditions
shows a favorable flatness of 3 .mu.m against the plate width of 20
mm, though the value is slightly larger than the value of the
example 9. Thus, it is found that when the heating is performed so
that the base material glass plate has a U-shaped temperature
distribution in the width direction, and the length of the base
material glass plate from a position where the melting starts to a
position of the inflection point formed at a time of the drawing on
the contour of the base material glass plate (i.e., meniscus
length) is equal to or longer than two-thirds the width of the base
material glass plate, a glass strip with an even more excellent
flatness can be manufactured.
The example 11 performs heating with the heating furnace using the
heaters with a relatively short heater length as shown in FIG. 7.
Through the similar temperature setting as in the example 9, a
U-shaped temperature distribution with the temperature difference
of 60.degree. C. between the central portion and the side portion
of the base material glass plate is obtained. Further, even though
the heater length is approximately a half that of the example 9,
the heat zone length is similar to that of the example 9, and the
meniscus length is 0.88 time the base material width similarly to
the example 9. A glass strip manufactured under such conditions
shows a highly favorable flatness of 1 .mu.m against the plate
width of 20 mm similarly to the example 9. In addition, the use of
the heaters with a relatively short heater length results in
efficient heating with lower power consumption.
When quartz glass is employed as a material of a glass strip in the
present invention, it is possible to deposit a functional film on a
surface of the glass strip through thermal CVD, for example,
utilizing a high-temperature tolerance thereof. Further, when
multicomponent glass is employed as a material of a glass strip, it
is possible to deposit a functional film on a surface using a
low-temperature process.
Still further, the glass strip of the present invention may be cut
off in a polygonal shape, a circular shape, or a disk shape
according to the use purpose, and used as a glass substrate.
Further, an obtained substrate may be polished before use.
INDUSTRIAL APPLICABILITY
A glass strip manufactured according to the method of manufacturing
a glass strip according to the present invention can be developed
into a product group utilizing the flatness and surface property
thereof. For example, the glass strip is useful as a material for
semiconductor devices, spacers for field-effect flat panel
displays, and circuit substrates, in particular, is appropriate for
substrates of semiconductor devices, spacers used in field-effect
flat panel displays, and substrates of small magnetic disks.
Further, glass substrates manufactured from glass strips of the
present invention are suitable for glass substrates of DNA chips
employed in medical analysis or the like. Further, when the glass
strips of the present invention are arranged in a planar-shape, the
glass strips can be expanded to two-dimensional substrates of any
size.
* * * * *
References